The article “Luminescence Lifetime Imaging of Oxygen, pH, and Carbon Dioxide Distribution Using Optical Sensors” by G. Liebsch, I. Klimant, B. Frank, G. Holst, and O. S. Wolfbeis in Applied Spectroscopy 54, Number 4 (2000), pages 548 to 559, describes the determination of various variables for samples in the wells of a microtitre plate via the dependence of the luminescence lifetime of substances used as sensors on the respective variable. It is not the luminescence lifetime itself which is determined, but a parameter depending on the luminescence behavior, wherein the parameter is calibrated against the variable to be determined.
U.S. Pat. No. 7,819,328 B2 relates to an optical identification element. This is assigned to an object and contains stored information on the object. The optical identification element includes an optical device which converts light incident from a reader into electrical energy. This energy is used for optical transmission of the information stored in the optical identification element to the reader. The stored information may for example be a retail price, counterfeit protection features, or sales restrictions.
U.S. Pat. No. 7,606,451 B2 discloses a communication system with at least one optical identification element and at least one optical reader. Between the reader and the identification element identification information is transmitted via light. The optical identification element has storing units for storing identification information, reflecting units for reflecting incident light, and modulating units for modulating the reflected light according to the stored identification information. Furthermore photoelectric converters are provided to supply the identification element with electrical energy from the incident light.
U.S. Pat. No. 7,229,023 B2 relates to an identification element with a transceiver for optical radiation and a transceiver for radio waves. The transceivers can be operated in different modes depending on the use of the identification element.
Optical methods for determining a variable by means of a sensor exhibiting an optical behavior depending on the variable are well known, the article cited above contains some, but in no way exhaustive, examples. In the article the sensors used are luminescence sensors, i.e. a respective sensor responds to an optical excitation with a luminescence phenomenon. In this application optical excitation means excitation with optical radiation, i.e. with electromagnetic radiation from the infrared to the ultraviolet spectral range; for this radiation here also the term light is used.
More generally speaking for the determination of a variable a sensor cooperates with optical radiation, and exhibits an optical behavior which depends on the variable. The optical radiation may for example impinge on the sensor as single light pulses, in series of light pulses, or as continuous illumination. A considerable advantage of such optical methods is that they are contactless methods, which for example may be carried out through a wall of a sample container which is transparent for the optical radiation used. Therein the sensor is in the sample container in contact with the sample; no electrical connections, which may be perturbing for some experiments, to the sensor are required. Such sensors also can easily be used with sterile containers; the sensors are put into the container before sterilisation, and are sterilised with the container. This greatly simplifies handling. Furthermore such sensors can be manufactured in relatively small a size; typically they have a diameter of about 5 mm and a thickness between 0.2 mm and 5 mm, there are also known examples of only 1 mm diameter. They therefore are considerably smaller than embodiments for example of commercial temperature sensors, like Pt100, which reach lengths of 3 cm and sometimes more, and which furthermore require electrical contacts.